alien: A non-native organism. (in astronomy) Life on or from a distant world.
asteroid: A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
astrobiology: The study of life everywhere in the universe, including on Earth and in space. A scientist who works in this field is known as an astrobiologist.
astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.
atmosphere: The envelope of gases surrounding Earth, another planet or a moon.
biology: The study of living things. The scientists who study them are known as biologists.
carbon: A chemical element that is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
Cassini: A space probe sent by NASA to explore the planet Saturn. Cassini was launched from Earth in 1997. It reached Saturn in late 2004. The craft included a variety of instruments meant to study Saturn’s moons, rings, magnetic field and atmosphere.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
cloud: A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents.
compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions.
cosmos: (adj. cosmic) A term that refers to the universe and everything within it.
crust: (in geology) Earth’s outermost surface, usually made from dense, solid rock (in planetary science) the outermost surface of rocky planets, dwarf planets and natural satellites.
debris: Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
disk: A round, flat and usually fairly thin object. (in astronomy) A rotating cloudlike collection of gases, dust or both from which planets may form. Or the structure of certain large rotating bodies in the cosmos, including spiral galaxies.
Enceladus: The sixth largest of Saturn’s 145 known moons. Enceladus is bright white and covered with a thick shell of ice. Deep beneath that ice sits what appears to be a global ocean of salty liquid water. Enceladus is a round sphere, roughly 500 kilometers (310 miles) across. It is a little less than one-third the width of Earth’s moon.
equator: An imaginary line around Earth that divides Earth into the Northern and Southern Hemispheres.
Europa: One of the 95 named moons of Jupiter and the sixth-closest satellite to the planet. Europa, 1,951 miles across, has a network of dark lines on a bright, icy surface.
exotic: An adjective to describe something that is highly unusual, strange or foreign (such as exotic plants).
field: An area of study, as in: Her field of research is biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory
force: Some outside influence that can change the motion of an object, hold objects close to one another, or produce motion or stress in a stationary object.
fuel: Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).
geologic: An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.
Grand Canyon: A natural canyon in northwest Arizona that formed as the Colorado River cut through the rock here over the past 5 million to 6 million years. This is one of many canyons on the river, which drains water from seven states. The Grand Canyon is 446 kilometers (277 miles) long. Its depth varies. At its deepest point, the river is 1,829 vertical meters (6,000 feet) below the upper rim. From rim to rim, the canyon’s width also varies — from about 16 kilometers (10 miles) to 29 kilometers.
gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
habitable: A place suitable for humans or other living things to comfortably dwell.
host: (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents. (v.) The act of providing a home or environment for something. A website, for instance, could host photos, news or other types of information.
hydrocarbon: Any of a range of large molecules containing chemically bound carbon and hydrogen atoms. Crude oil, for example, is a naturally occurring mix of many hydrocarbons.
hydrothermal vent: An opening at the bottom of the ocean or a lake where hot water emerges from deep inside Earth. The water is rich in minerals and chemicals that can nourish ecosystems of worms, clams, microbes and other organisms.
Jupiter: (in astronomy) The solar system’s largest planet, it has the shortest day length (9 hours, 55 minutes). A gas giant, its low density indicates that this planet is composed mostly of the light elements hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).
magma: The molten rock that resides under Earth’s crust. When it erupts from a volcano, this material is referred to as lava.
magnetic field: An area of influence created by certain materials, called magnets, or by the movement of electric charges.
Mars: The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
Mercury: (in astronomy and here the term is capitalized) The smallest planet in our solar system and the one whose orbit is closest to our sun. Named after a Roman god (Mercurius), one year on this planet lasts 88 Earth days, which is shorter than one of its own days: Each of those lasts 175.97 times as long as a day on Earth.
methane: A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas.
mineral: Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).
molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
moon: The natural satellite of any planet.
moonmoon: The term for a moon that orbits a moon.
NASA: Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.
nitrogen: A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth’s atmosphere. Its scientific symbol is N.
orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.
organic: (in chemistry) An adjective that indicates something is carbon-containing; also a term that relates to the basic chemicals that make up living organisms.
oxygen: A gas that makes up about 21 percent of Earth’s atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
particle: A minute amount of something.
physics: The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.
planetary science: The science of planets other than Earth.
plume: (in biology) A single large feather. (in environmental sciences) The movement of some gas or liquid, under the direction of gravity, winds or currents. It may be in air, soil or water. It gets its name from the fact that it tends to be long and relatively thin, shaped like a large feather. (in geology) Fluids (air, water or magma typically) that move, largely intact, in a feather-like shape over long distances.
Pluto: A distant world that is located in the Kuiper Belt, just beyond Neptune. Known as a dwarf planet, Pluto is the ninth largest object orbiting our sun.
propulsion: The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.
radiation: (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
Red Planet: A nickname for Mars.
Saturn: The sixth planet out from the sun in our solar system. One of the two gas giants, this planet takes 10.6 hours to rotate (completing a day) and 29.5 Earth years to complete one orbit of the sun. It has at least 145 named moons. But what most distinguishes this planet is the broad and flat plane of bright rings that orbit it.
sea: An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
simulate: To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb.
smog: A kind of pollution that develops when chemicals react in the air. The word comes from a blend of “smoke” and “fog,” and was coined to describe pollution from burning fossil fuels on cold, damp days.
solar system: The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
soot: Also known as black carbon, it’s the sometimes oily residues of incompletely burned materials, from plastics, leaves and wood to coal, oil and other fossil fuels. Soot particles can be quite small — nanometers in diameter. If inhaled, they can end up deep within the lung.
star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun: The star at the center of Earth’s solar system. It is about 27,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body’s circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation’s railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.
technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
theory: (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
vent: (n.) An opening through which gases or liquids can escape. (v.) To free gases or liquids that had been under pressure.
Venus: The second planet out from the sun, it has a rocky core, just as Earth does. Venus lost most of its water long ago. The sun’s ultraviolet radiation broke apart those water molecules, allowing their hydrogen atoms to escape into space. Volcanoes on the planet’s surface spewed high levels of carbon dioxide, which built up in the planet’s atmosphere. Today the air pressure at the planet’s surface is 100 times greater than on Earth, and the atmosphere now keeps the surface of Venus a brutal 460° Celsius (860° Fahrenheit).
volcano: A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations.
Voyager: A pair of NASA missions conducting close-up explorations of Jupiter, Saturn, Saturn’s rings and the larger moons of the both large planetary gas giants. The Voyager 2 craft launched Aug. 20, 1977 — 16 days earlier than Voyager 1. As of the writing of this story, both craft were still working and had exited the solar system, now flying through deep space.
water vapor: Water in its gaseous state, capable of being suspended in the air.
